Monitoring of intracranial pressure can be accomplished by several methods. The most widely used techniques involve inserting a catheter in the lateral ventrical or introducing a hollow screw-like device through the skull into the subarachnoid space.
The concept of using hollow screw-like devices to measure and continuously monitor intracranial pressure was introduced in 1971 by Vries and Becker. Their invention is called the "Richmond screw". The basic principle involved in use of a hollow screw device involves providing a fluid connection means from the fluid in the patient's head (the subarachnoid fluid or cerebrospinal fluid (CSF)) to an external pressure sensing system. This is shown schematically in FIG. 2. The screw device screws into the skull and allows CSF to pass through its internal channel to a connection tube and on to a pressure transducer and monitor. The measurement of the fluid pressure then indicates the patient's intracranial pressure (ICP).
The measurement and continuous monitoring of intracranial pressure has been useful clinically. However, the currently used devices can be unstable, do not insure accurate placement of the screw tip in the subarachnoid space, are not designed to prevent accidental plunging of the device through the drill hole into the brain and do not offer the ability to adjust the depth of the screw based on exact measurement of skull thickness and depth of the subarachnoid space.
Another recent design of a screw-like device called the "Philly Bolt" is offered with a fixed flange above its distal threaded portion (FIG. 3). Again since there is no adjustability of the distance from the tip end to flange, exact placement of the tip to the subarachnoid space is often not possible. For this reason, a variety of different lengths of "Philly Bolt" must be available to accomodate different skull thicknesses. Thus this design has the disadvantages of inexact placement of its tip to the subarachnoid space and non-universality of length.
The present invention is a device that is used in the measurement and continuous monitoring of intracranial pressure. The device will be referred to herein as the Swann-Cosman Bolt. It is a screw-type device which can be screwed into a hole in the skull to allow subarachnoid fluid to be coupled to a fluid tubing which in turn is connected to a pressure sensor for measuring the fluid pressure. The device has several novel features which overcome the problems of previous designs.
The basic objectives of this invention are to provide a device that features (1) increased stability within the skull, (2) increased safety with a device to prevent plunging into the brain during and after insertion into the skull, (3) adjustability to the varied skull thicknesses found among patients, (4) the ability to accurately measure the depth of the subarachnoid space with a depth gauge and to place the tip of the device exactly at the desired location, (5) design elements to prevent plugging of the device during insertion such as a metallic stylette and (6) a female luer port that allows the easy attachment of only one stopcock to the device.
The accompanying drawings show examples of prior art and embodiments of the present invention. They illustrate how the invention achieves the above stated advantages and objectives.